Process of rephosphorizing steel.



' from basic open-hearth steel much trouble is UNITED STATES PATENT OFFICE.

JOHN STEVENSON, JR., OF SHARON, PENNSYLVANIA.

PROCESS OF REPHOSPHORIZING STEEL.

SPECIFICATION forming part of Letters Patent No. 724,140, dated March 31, 1903.

Application filed February 1, 1902.

To all whom it may concern:

Be it known that I, JOHN STEVENSON, Jr., of Sharon, Mercer county, Pennsylvania, have invented a new and useful Process of Rephosphorizing Steel, of which the following is a full, clear, and exact description.

In the manufacture of tin plate and sheets encountered in the process of opening or split ting the black sheets from the doubled and rolled packs, due to the sticking of the sheets one to another. This does not take place with Bessemer steel, a steel containing a higher percentage of phosphorus than basic steel, as in the process of manufacturing basic steel this element is largely removed. It has been found that no element so influences or tends to nullify the sticking of the sheets as the presence of phosphorus. Hence it has necessitated in the manufacture of basic tin plate or sheets the finding of some means of restoring or adding phosphorus to the steel to overcome this difficulty. This has been done hitherto by adding to the steel as it issues from the open-hearth furnace a phosphoritic material, the most suitable of which until recently has proven to be a phosphatic limestone or apatite; The use of this material has not proven satisfactory for several reasons.

First. The small percentage of phosphorus contained therein, minerals of this sort not containing over fourteen to fifteen per cent. phosphorus.

Second. The phosphorus is present as phosphoric acid or in the oxidized condition and in combination-with lime, in which condition it does not readily unite with steel, as phos phorus is found only in the steel in the condition of a phosphide. This requires that the phosphoric acid be reduced or deprived of its oxygen before entering the steel, and since the steel when tapped from the furnace is oxygenated or full of occluded gases the reduction of the phosphorus is not apt to take place to any considerable extent, giving rise to irregular product and the loss of a large" percentage of the available phosphorus.

Third. This reduction of the phosphorus can only take place through the combination of the accompanying oxygen with some other element, and this is usually at the expense of Serial No. 92,149. (No specimens.)

the manganese or the carbon that is added at the time of tapping to remangauize and recarburize, again resulting in the irregular product.

Fourth. In order that the largest possible surface of the apatite may be exposed to the molten steel for taking up the phosphorus to any extent, it is necessary to finely pulverize the apatite, with the result that a great deal of it is lost by being driven out of the ladle by the commotion caused by the incoming steel, likewise causing irregularity in the product.

Fifth. In order that any phosphorus taken up by the steel may not again be removed by contact with the slag that drains from the furnace upon the metal in the ladle, causing much ebullition, it is necessary to work the heat in the furnace with as silicious a slag as possible, as a calcareous slag has a great affinity for phosphorus. This results in a high sulfur steel. Sulfur has no affinity for a silicious slag, and unless the slag is calcareous enough to remove phosphorus it will not act radically upon the sulfur. Thus the conditions favoring the two reactions desired are directly opposed to one another.

' Sixth. Since the amount of phosphorus taken up by the steel from the apatite is small and as a large percentage of the apatite is lost, as before stated, on account of its pulverulent'condition, it becomes necessary in order to obtain the requisite amount of phosphorus in the steel to use a very large quantity of the apatite, with the result that so much cold material is added to the hot bath of metal as to chill it considerably, and thus cause trouble in the teeming or pouring.

Seventh. To overcome this last difficulty, it is necessary to tap the steel at a much higher temperature than usual, which superheatiug destroys the quality of the steel, causing it to become oxygenated and full of cocluded gases. This makes the steelred-short,

' so that it cracks in rolling, and, furthermore,

the gases cause blow-holes to form during the solidification of the ingot. These blow-holes result in blisters in the finished sheet, so that with the cracks and the blisters the material is unfit for many purposes and the source of much less.

The foregoing difficulties have been some- IOU what overcome by the rephosphorization of the steel by a pig metal high in phosphorus, called ferrophosphorus. Its use while it overcomes some of the trouble does not remove all, and in addition it complicates the conditions somewhat. For instance, ferromanganese is used to recarburize the steel and at the same time by the addition of the manganese induce in the steel the property of rolling without cracking. The ferrophosphorus is of necessity added at the same time, both being added when the metal is being tapped into the ladle to avoid loss of the elements carbon, manganese, and phosphorus by oxidation. The addition of the ferromanganese itself has a tendency to chill the bath, which effect is further increased by the addition of the ferrophosphorus, for in order that the elements carbon, manganese, and phosphorus can enter the steel the amount of heat absorbed must be sufficient to thoroughly liqnefy the cold ferrophosphorus and ferromanganese. Again, as ferrophosphorus contains a considerable amount of carbon this is of necessity taken up by the bath, for which allowance must be made in the carbon content of the bath in addition to that introduced by the ferromanganese. As the loss of available carbon varies according to the condition of the bath, this means the introduction of two variable factors in the final result. I have found that these difficulties in the manufacture of basic steel for tin plate and sheets can be overcome by the use in recarburizing and rephosphorizing of a metallurgical product which may be described as a phosphoric ferromanganesean alloy combining in one the uses and properties of both ferrophosphorus and ferromanganese. In ferrophosphor-manganese the elements desired in the steel for the manufacture of tin plate and sheets-viz., phosphorus and carbon and manganese-are concentrated to a high percentage, and the medium by which they are bonded-the inert ironis reduced in quantity. By its use improved results are obtained for the following reasons:

First. One addition only is necessarily made to the molten metal, and by reason of the concentration of the elements phosphorus, carbon, and manganese this addition is much less in amount than has previously been called for with the two or more separate additions when ferrophosphorus and ferromanganese are used.

Second. The amount of inert material being thus reduced, the chilling effect on the molten steel is correspondingly diminished, so that the metal can be tapped at a much lower temperature than hitherto-a most dosirable gain.

Third. The recarburizing is much simplified, as the carbon being added in one addition the losses of that metalloid can be more closely observed and the proper provision made in the carbon content of the molten steel.

Fourth. Being enabled to tap the heat ata lower temperature through the use of this alloy, a greatly-increased uniformity of quality in product is obtained. The loss by oxidation of the elements phosphorus, carbon, and manganese is diminished, as the lower the temperature at which the steel has been produced the less oxygenated its condition. Likewise the irregularity in product due to segregation of the phosphorus, carbon, sulfur, and manganese is lessened, as nothing is more conductive to the liquation of these elements in the steel than a high temperature.

Fifth. The cost of the process is much reduced, the amount of the alloy required being lessened and the cost of same being lower than either ferromanganese or ferrophosphorus.

The proportions of each element in the al- 10y may be varied widely without departing from my invention.

I claim 1. The method of rephosphorizing iron or steel, consisting in adding thereto an alloy of iron, phosphorus and manganese; substantially as described.

2. The method of rephosphorizing basic steel and at the same time recarburizing the same, consisting in adding thereto an alloy of iron, containing a high proportion of phosphorus, carbon and manganese; substantially as described.

3. The method of rephosphorizing and recarburizing basic steel, consisting in tapping the steel from an open-hearth furnace and adding thereto an alloy of iron containing a high proportion of phosphorus, carbon and manganese; substantially as described.

In testimony whereof I have hereunto set my hand.

JOHN STEVENSON, J R.

VVit-nesses:

K. J. STEINER, E. II. WARD.

ICC 

